I think your boiler does modulate, probably down to 5 or 6 kw but not 100% sure.
I think you were reasonably happy a few months ago with CP1@ 3M and are now running with CP2 @4.5M, I would say either of those, whichever gives you all rads heating equally etc, my system, similar to yours runs at a 3M head equivalent, in PP mode set to 4.3M. Your system should run quite well with a 3M head if its reasonably clean.
ABV setting: I would be very surprised if your heating engineer set the ABV to 0.3 on CC iii (6M) is this would result in a huge recirculation rate of ~ 14/16 LPM, greater than your system demand which would result in a much higher boiler return temp and reducing boiler efficiency, on CP2 setting (4.5M) you would still be recirculating ~ 11 LPM with the ABV set to 0.3, I would say, based on the pump power of 35W on CP2 that the ABV is full of crap and not recirculating anything as I would have expected a power demand of ~ 42W on CP2, IF the ABV is clear and you wish to remain on CP2(4.5M) then suggest setting the ABV to 0.43 which may give you a minimum flow rate of 3 or 4 LPM. If happy to run with CP1 (3M) then set the ABV to 0.28.
If running on CP2 (4.5M) just now then the outlet pipe from the ABV should be roasting at that setting of 0.3 so adjust as required for CP2 or CP1 as appropriate.
Practically, you probably should just set it slightly higher initially and then very very gradually keep reducing the index until you just feel the by pass outlet getting hot, ie on CP2 set to 0.50 and then gradually reduce, on CP! set to 0.35 and do ditto.